Colored encapsulated liquid crystal apparatus using enhanced scattering

ABSTRACT

The present invention relates to use of liquid crystal material encapsulated in a containment medium to produce a controlled colored output, for example, in response to the application, removal and variation in an electric field. In one embodiment a non-pleochroic dye is in the containment medium itself and in another embodiment the non-pleochroic dye is in the liquid crystal material itself; and in both cases the object is to color light. Incident light impinging on the encapsulated liquid crystal material, which is mounted on, in, or with respect to a support medium, is isotropically scattered in the absence of an electric field, and using the principle of total internal reflection (or optical interference or both) a relatively large part of the isotropically scattered light in the support medium is reflected back to illuminate the scattering liquid crystal material, which isotropically scatters such light again, thus increasing the optical path through the dyed material and, therefore, the coloring of the light traveling such increased path. Light scattered back to the viewing direction out of the support medium causes the liquid crystal material to appear relatively bright and colored as compared to the background where there is no liquid crystal material or where the liquid crystal material is in parallel alignment in field-on condition, i.e., substantially transmissive.

This application is a division of Ser. No. 480,466, filed Mar. 30, 1983,which is now U.S. Pat. No. 4,596,445.

CROSS REFERENCE TO RELATED APPLICATION

Reference is also made to applicant's copending, commonly assigned U.S.patent application Ser. No. 302,780, filed Sept. 16, 1981, for"Encapsulated Liquid Crystal and Method" now U.S. Pat. No, 4,435,047;U.S. patent application Ser. No. 477,242, filed Mar. 21, 1983, for"Encapsulated Liquid Crystal and Method", now U.S. Pat. No. 4,616,903;U.S. patent application Ser. No. 477,138, filed Mar. 21, 1983, for"Enhanced Scattering in Voltage Sensitive Encapsulated Liquid Crystal";and U.S. patent application Ser. No. 480,461, concurrently filedherewith, for "Colored Encapsulated Liquid Crystal Devices UsingImbibition Of Colored Dyes And Scanned Multicolor Displays", now U.S.Pat. No. 4,662,720. The entire disclosures of such applications arehereby incorporated by reference.

TECHNICAL FIELD

The present invention relates generally to the art of liquid crystals,to the producing of a color output of a liquid crystal device, and, moreparticularly, to the scattering of light by liquid crystal material andreflection of the scattered light to increase the optical path length inthe liquid crystal apparatus to enable coloring of the light usingnon-pleochroic dye. Moreover, the invention relates to usingencapsulated liquid crystal or liquid crystal material held in acontainment medium, such as an emulsion, with dye in the containmentmedium, and/or in the support medium therefor. The invention alsorelates to use of non-pleochroic dye in the liquid crystal material.Additionally, the invention relates to use of a fluoroescent dye in aliquid crystal device. The invention further relates to methods ofmaking and using such liquid crystal apparatus.

BACKGROUND

Liquid crystal material currently is used in a wide variety of devices,including, for example, optical devices such as visual displays. Aproperty of liquid crystals enabling use in visual displays is theability to scatter and/or to absorb light when the liquid crystals arein a random alignment and the ability to transmit light when the liquidcrystals are in an ordered alignment.

Frequently a visual display using liquid crystals displays darkcharacters on a gray or relatively light background. In variouscircumstances it would be desirable, though, using liquid crystalmaterials to be able to display with facility relatively bright coloredcharacters or other information, etc. on a relatively dark background.It would be desirable as well to improve the effective contrast betweenthe character displayed and the background of the display itself.

An example of electrically responsive liquid crystal material and usethereof is found in U.S. Pat. No. 3,322,485. Certain types of liquidcrystal material are responsive to temperature, changing the opticalcharacteristics, such as the random or ordered alignment of the liquidcrystal material, in response to temperature of the liquid crystalmaterial.

Currently there are three categories of liquid crystal materials, namelycholesteric, nematic and smectic. The present invention preferably usesnematic liquid crystal material or a combination of nematic and somecholesteric type. More specifically, the liquid crystal materialpreferably is operationally nematic, i.e. it acts as nematic materialand not as the other types. Operationally nematic means that in theabsence of external fields structural distortion of the liquid crystalis dominated by the orientation of the liquid crystal at its boundariesrather than bulk effects, such as very strong twists as in cholestericmaterial, or layering as in smectic material. Thus, for example, chiralingredients which induce a tendency to twist but cannot overcome theeffects of boundary alignment still would be operationally nematic. Suchmaterial should have a positive dielectric anisotropy. Although variouscharacteristics of the various liquid crystal materials are described inthe prior art, one known characteristic is that of reversibility.Particularly, nematic liquid crystal material is known to be reversible,but cholesteric material ordinarily is not reversible.

It is also known to add pleochroic dyes to the liquid crystal material,for example, for increasing absorption characteristics. However, in thenematic form a pleochroic device has relatively low contrast. In thepast cholesteric material could be added to the nematic materialtogether with the dye to improve contrast ratio. See for example theWhite et al article in Journal of Applied Physics, Vol. 45, No. 11,November 1974, at pages 4718-4723. However, although nematic material isreversible, depending on whether or not an electric field is appliedacross the same, cholesteric material ordinarily would not tend to itsoriginal zero field form when the electric field would be removed.Another disadvantage to use of pleochroic dye in solution with liquidcrystal material is the the absorption of the dye is not zero in thefield-on condition; rather, absorption in the field-on condition followsan ordering parameter, which relates to or is a function of the relativealignment of the dyes. Moreover, pleochroic dyes are relativelyexpensive and must be used carefully, usually having to be mixeddirectly in the liquid crystal material itself.

Usually liquid crystal material is anisotropic both optically(birefringence) and, for example in the case of nematic material,electrically. The optical anisotropy is manifest by the scatteringand/or absorption (especially when pleochroic dye is in solution withthe liquid crystal material) of light when the liquid crystal materialis in random alignment, and the transmission of light through the liquidcrystal material when it is in ordered alignment. The electricalanisotropy may be a relationship between the dielectric constant ordielectric coefficient with respect to the alignment of the liquidcrystal material.

In the past, devices using liquid crystals, such as visual displaydevices, have been relatively small. Use of encapsulated liquid crystalsdisclosed in applicant's above mentioned co-pending applications hasenabled the satisfactory use of liquid crystals in relatively large sizedisplays, such as billboards, etc., as is disclosed in such application;and another large (or small) scale use may be an optical shutter tocontrol passage of light from one area into another, say at a window orwindow-like area of a building. The present invention relates toimprovements in such encapsulated liquid crystals and to the utilizationof the light scattering characteristic of the liquid crystal materialand reflection, e.g. by total internal reflection and/or opticalconstructive interference, of the scattered light to increase opticalpath length in a material containing a relatively small quantity ofpreferably standard or other non-pleochroic dye. The increased pathlength through the dye assures the desired coloring of ouptut light. Theinvention also relates to the use of such material and characteristics,for example, to obtain a relatively bright colored character orinformation displayed on a relatively dark or colored background in bothsmall and large displays, optical shutters, and so on. Such largedisplays, shutters, etc. may be about one square foot surface area oreven larger. In accordance with the present invention the liquid crystalmaterial most preferably is of the encapsulated type.

As used herein with respect to the present invention, encapsulatedliquid crystal material means liquid crystal material in a substantiallyclosed containment medium, such as discrete capsules or cells, andpreferably may be in the form of an emulsion of the liquid crystalmaterial and the containment medium. Such emulsion should be a stableone. Various methods for making and using encapsulated liquid crystalmaterial and apparatus associated therewith are disclosed below and inapplicant's copending applications, which are incorporated by reference.

To facilitate comprehension of the invention relative to conventionalprior art liquid crystal displays, one typical prior art display isdescribed here. Such a prior display may include a support medium andliquid crystal material supported thereby. The display is relativelyflat and is viewed from a viewing side or direction from which aso-called front or top surface of the display is viewed. The back orbottom surface of the support medium may have a light reflective coatingtending to make the same appear relatively bright in comparison torelatively dark characters formed at areas where there is liquid crystalmaterial. (Back, front, top, bottom, etc. are used herein in general andwith reference to the drawings only for convenience; there is noconstraint that in operation the viewing direction must be, for example,from only the top, etc.). When the liquid crystal material is in orderedalignment, for example in response to application of an electric fieldthereto, incident light from the viewing direction passes through theliquid crystal material to the light reflective coating and also wherethere is no liquid crystal material passes directly to the lightreflective coating; and no character is observed from the viewingdirection. However, when the liquid crystal material is in randomalignment, it will absorb some and scatter some incident light therebyto form a relatively dark character on a relatively light colorbackground, for example of gray or other color depending on the type oflight relfective coating mentioned above, which still continues toreflect incident light where there is no liquid crystal material orwhere some liquid crystal material is in ordered alignment. In this typeof display it is undesirable for the liquid crystal material to scatterlight because some of that scattered light will be directed back in theviewing direction thereby reducing the darkness or contrast of thecharacter relative to the background of the display. Pleochroic dyeoften is added to the liquid crystal material to increase absorbenceand, thus, contrast when the liquid crystal material is in randomalignment.

BRIEF SUMMARY OF INVENTION

Succinctly stated, the disclosure relates to the producing of a coloredoutput by a liquid crystal device which uses non-pleochroic dye, and toisotropic scattering and reflecting of isotropically scattered light inthe device to increase the path length through the dye to yield arelatively bright colored appearance, character, information, etc.,especially relative to background, when a liquid crystal material is ina field-off or distorted alignment condition and a different colored ordark appearance, e.g., the same as background, when the liquid crystalmaterial is in field-on parallel or ordered alignment condition.Preferably the liquid crystal material is nearly completelyisotropically scattering when in distorted alignment. Isotropicscattering means that when a beam of light enters the liquid crystalmaterial there is virtually no way to predict the exit angle ofscattered light.

Importantly, the dye is in the containment medium, in the supportmedium, or in the liquid crystal material and need not be of thespecialized pleochroic type. The dye should be soluble, and thus,dissolved, in the medium containing same. For example, a water solubledye may be dissolved in a water base polyvinyl alcohol containmentmedium, and/or an oil soluble dye may be dissolved in an oil base liquidcrystal material.

Coloring of the visual or optical output is due to the increased pathlength of the isotropically scattered light in the support medium due tothe reflection, preferably totally internal reflection, therein. Somelight not totally internally reflected in the support medium will exit aviewing surface thereof to effect the colored character display oroutput.

An advantage of applying the dye to the support medium and not to theliquid crystal is that a universal base stock of encapsulated liquidcrystal may be manufactured, stored and used, when needed, inconjunction with a dyed support medium of any color to achieve thedesired color display.

An advantage to use of fluorescent dye is the effective or apparentlight amplification due to light emitted by the fluorescent dye inresponse to incident light or possibly other radiation.

As it is used herein with respect to the invention, the terms distortedalignment, random alignment and field-off condition means essentiallythe same thing; namely, that the directional orientation of the liquidcrystal molecules is distorted to an effectively curved configuration.Such distortion is effected, for example, by the wall of respectivecapsules. The particular distorted alignment of liquid crystal materialin a given capsule usually always will be substantially the same in theabsence of an electric field.

On the other hand, as it is used herein with respect to the invention,parallel aligned, ordered alignment, and field-on condition means thatthe liquid crystal material in a capsule is generally aligned withrespect to an extnerally applied electric field.

In accordance with one aspect of the present invention, a liquid crystaldisplay can product relatively bright colored characters, information,etc., on a relatively dark background; the bright colored character isproduced by liquid crystal material that is randomly aligned. Themultiple passes of light through the dyed material, which is not of thepleochroic type, satisfactorily colores the light output of the display,optical shutter, etc. The background is caused, for example, by liquidcrystal material that is in ordered alignment and, thus, substantiallyoptically transparent and/or by areas of the display where there is noliquid crystal material. When the liquid crystal material is in parallelor ordered alignment, only the relatively dark background, e.g., formedby an absorber, would appear. The foregoing is accomplished usingrelatively low power requirements, minimum liquid crystal material, andillumination either from the viewing side or direction or from the backor non-viewing side of the display. The principles of the invention alsomay be used in an optical shutter or light control device to controlbrightness, for example.

Briefly, the liquid crystal apparatus includes liquid crystal materialfor selectively primarily scattering or transmitting light in responseto a prescribed input and a support medium for holding therein orsupporting thereon the liquid crystal material. In accordance with aprferred embodiment and best mode of the invention, the liquid crystalmaterial is of the encapsulated type, e.g., liquid crystal material in acontainment medium, and such encapsulated liquid crystal is positionedin or mounted on a support medium. Alternatively, the containment mediumitself may form or be part of the support medium. Such encapuslatedliquid crystal material will cause substantially isotropic scattering oflight incident thereon, including the scattering of some of such lightback in the viewing direction toward, for example, the eye of anobserver. More preferably, such liquid crystal is operationally nematic,has a positive dielectric anisotropy, and has an ordinary index ofrefraction that substantially matches that of the containment orencapsulating medium therefor.

In one embodiment, a large quantity of light that is isotropicallyscattered by the liquid crystal material is totally internally reflectedby the support medium back to the liquid crystal material therebyilluminating the same and causing further isotropic scattering andbrightening of the appearance of the liquid crystal material, forexample to the eye of an observer. The extensive path length of light inthe support medium, containment medium, and/or liquid crystal materialitself and the dye carried by one or more thereof assures the desiredcoloring of the light to give a colored output appearance when thestructure of the liquid crystal is in a random or distorted alignment inthe absence of an electric field. The internal reflectancecharacteristic of the support medium may be effected by the interface ofsuch back surface with another medium, such as a solid, liquid, or gas,even including air, with the constraint that the index of refraction ofthe support medium is greater than the index of refraction of such othermedium. The support medium may be comprised of several components,including, for example, the containment/encapsulating material (or thatwith which the liquid crystal material is in emulsion), additionalquantities of such encapsulating or other material, a mounting medium,such as a plastic-like film or glass, etc., all of which will bedescribed in further detail below.

The back surface of the support medium may be optically transmissive sothat light that reaches such surface in a direction substantially normalthereto will be transmitted. A light absorbing black or colored materialbeyond such back surface can help darken or color the apparentbackground on which the characters formed by liquid cyrstal materialappear. Ordered alignment of the liquid crystal material will at leastsubstantially eliminate the isotropic scattering so that substantiallyall the light passing through the liquid crystal material will also passthrough the back surface of the support medium.

In an alternate embodiment, a tuned dielectric coating may be applied,e.g. by evaporation techniques, to the back surface of the supportmedium to effect selective constructive and destructive opticalinterference. The thickness of such tuned dielectric coating will be afunction of lambda (λ) divided by 2, lambda being the wavelength oflight employed with the apparatus. Constructive interference willenhance the internal reflection, especially by reducing the solid anglewithin which light would not be totally internally reflected in thesupport medium; and, therefore, such interference will further brightenand intensify the color of the appearance of the liquid crystal materialcharacters.

Incident illumination for a liquid crystal display embodying theinvention may be from the front or viewing side. Alternatively, incidentillumination may be from the back side, preferably through a mask ordirector to direct light fully transmitted by the liquid crystalmaterial out of the field or angle of view at the viewing side. However,light scattered by the liquid crystal material within the viewing anglewould be seen.

Moreover, a cholosteric material may be added to the nematic liquidcrystal material to expedite return of the latter to distorted alignmentpattern following in general the configuration of the capsule or cellwall when the electric field is turned off, especially when the capsulesare relatively large. Also, if desired, a viscosity controlling additivemay be mixed with the liquid crystal. Further, an additive to the liquidcrystal may be used to help force a preferred alignment of the liquidcrystal structure in a capsule.

These and other embodiments of the invention will become apparent as thefollowing description proceeds.

A primary object of the present invention is to provide improvements inliquid crystal aparatus to provide colored output.

Another primary object is to effect selective substantially isotropicscattering of light using crystal material, especially of theoperationally nematic type, to reflect such scattered light, and tocolor such light) especially using non-pleochroic dye.

Still another primary object is to provide the various features andobjects of the invention in large size displays, in relatively smallsize displays and in optical shutters or other light control devices.

Even another primary object is to use non-pleochroic dye in a liquidcrystal optical apparatus, especially with such dye being in thecontainment medium, for encapsulating liquid crystal material, in suchliquid crystal material itself, and/or in a support medium for theencapsulated liquid crystal material.

Another object is to enhance the colored optical output of liquidcrystal apparatus.

An additional object is to display bright colored characters,information or the like on a relatively dark background using liquidcrystal apparatus.

A further object is to use the principle of total internal reflection toenhance operation of liquid crystal apparatus, particularly a liquidcrystal display, and especially to enhance the use of isotropicallyscattered light cooperating to increase the path length of light in theliquid crystal device and through non-pleochroic dye contained therein.

Even another object is to use the principles of optical interference toenhance the optical output of a liquid crystal apparatus, particularly aliquid crystal display.

Even an additional object is to scatter light isotropically in a liquidcrystal apparatus and to use such isotropically scattered light tocreate a bright colored character on a relatively dark background.

Even a further object is to improve the contrast of a liquid crystalapparatus.

Still another object is to improve the versatility of liquid crystaloptical devices.

Still an additional object is to provide a method for making a liquidcrystal apparatus.

Still a further object is to use colored liquid crystal apparatus insmall and large scale devices, especially employing encapsulated liquidcrystal material.

Yet another object is to provide incident illumination for a liquidcrystal device from the non-viewing side thereof, and especially toprovide bright colored characters, information, or transmitted lightrelative to background when using such illumination.

Yet an additional object is to facilitate and/or to expedite the returnof encapsulated operationally nematical liquid crystal material to afield-off random or distorted alignment.

Yet a further object is to minimize the amount of liquid crystalmaterial required for a particular function, optical device, etc.

Even another object is to help force the liquid crystal structure in acapsule to a preferred orientation therein when in a field-offcondition.

Even an additional object is to amplify light isotropically scattered ina liquid crystal apparatus using a fluorescent dye.

Even a further object is to use a fluorescent dye in a liquid crystaldevice.

These and other objects and advantages of the present invention willbecome more apparent as the following description proceeds.

To the accomplishment of the foregoing and related ends the invention,then, comprises the features hereinafter fully described andparticularly pointed out in the claims, the following description andthe annexed drawings setting forth in detail certain illustrativeembodiments of the invention, these being indicative, however, of but afew of the various ways in which the principles of the invention may beemployed.

BRIEF DESCRIPTION OF DRAWINGS

In the annexed drawings:

FIG. 1 is a schematic representation of a liquid crystal device inaccordance with the present invention;

FIGS. 2 and 3 are enlarged schematic illustrations of a liquid crystalcapsule in accordance with the present invention respectively under ano-field or field-off condition and under an applied electric field orfield-on condition;

FIGS. 4 and 5 are schematic representations of a liquid crystalapparatus according to one embodiment of the invention, respectively ina no-field condition and in an applied electric field condition;

FIG. 6 is a schematic representation of another embodiment of a liquidcrystal apparatus in accordance with the present invention using an airgap to cause total internal reflection;

FIGS. 7 and 8 are schematic representations of another embodiment ofliquid crystal apparatus in accordance with the present inventionemploying optical interference principles respectively under a no-fieldcondition and under an applied electric field condition;

FIG. 9 is an isometric view of a liquid crystal display apparatus inaccordance with the present invention and which may be formed of any ofthe embodiments disclosed herein;

FIG. 10 is a fragmentary schematic elevation view of another embodimentof liquid crystal apparatus using continuous layers of liquid crystalmaterial and interrupted electrodes;

FIG. 11 is a schematic isometric view, partly broken away, of theembodiment of FIG. 10;

FIG. 12 is a schematic view of an approximately proportioned liquidcrystal display according to the invention showing a more accuratelyrepresentative size relationship of the support medium layers andencapsulted liquid crystal layer for the several embodiments herein;

FIG. 13 is a schematic illustration of a nematic liquid crystal capsulewith cholosteric material additive, which may be used with the severalembodiments herein;

FIGS. 14 and 15 are schematic illustrations of still another embodimentof liquid crystal apparatus with a light control film director providedwith incident illumination from the non-viewing side, respectively, inthe field on and field off conditions;

FIG. 16 is a schematic illustration similar to FIGS. 14 and 15 but withthe light control film director cemented to the support medium;

FIG. 17 is a schematic illustration like FIGS. 2 and 3 showing analternate embodiment of encapsulated liquid crystal; and

FIG. 18 is a view like FIG. 6 but showing an embodiment usingfluorescent dye.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring in detail to the drawings, wherein like reference numeralsdesignate like parts in the several figures, and initially to FIGS. 1, 2and 3, encapsulated liquid crystal material used in accordance with thepresent invention is illustrated. In FIG. 1 is a schematicrepresentation showing non-pleochroic dye 9 in a liquid crystalapparatus 10 in accordance with the present invention. Throughout thedrawings such dye is represented by "X"-like marks; for clarity onlyseveral of such marks are shown, but it will be appreciated that suchdye preferably is generally uniformly or otherwise in a known orspecified way distributed in the respective medium or material in whichit is contained.

The apparatus 10 includes encapsulated liquid crystal material 11represented by a single capsule in FIGS. 1-3. Although the capsulesillustrated in the drawings are shown in two dimensions and, therefore,planar form, it will be appreciated that the capsules are threedimensional, most preferably spherical . The capsule 11 is shown mountedin a preferably generally transparent support medium 12 having upper andlower portions 12a, 12b which may be integral with each other. Theapparatus 10 also includes a pair of electrodes 13, 14 for applying anelectric field across the liquid crystal material when a switch 15 isclosed to energize the electrodes from a conventional voltage source 16.

The dye 9 may be in one or more of the support medium 12, and,preferably, the containment medium 33 (described further below). It alsomay be in the liquid crystal material 30. Moreover, it is preferablythat the dye be soluble in the material or medium containing same,especially to avoid the problem of the dye precipitating out of thematerial or medium and preferably to achieve the desired uniformity orcontrolled distribution of the dye.

A primary feature of the present invention is that such encapsulatedliquid crystal material will isotropically scatter light impingingthereon when in a field-off random alignment condition; and in thefield-on orderly aligned condition, such material will be substantiallyoptically transparent.

It is to be understood that the capsule 11 may be one of many capsulesthat are discretely formed or, more preferably, that are formed bymixing the liquid crystal material with a so-called encapsulatingmaterial or containment medium to form an emulsion, preferably a stableone. The emulsion may be applied to or sandwiched between the supportmedia portion 12a, 12b, and electrodes 13, 14, as is illustrated. Ifdesired, the support medium 12 and the so-called encapsulating materialor containment medium may be the same material. As a furtheralternative, the upper end lower support medium portions 12a, 12b, orone of them, may be a plastic-like, glass, or like, preferablytransparent, mounting material. As used herein, transparent still allowsthe possibility of dye being contained in the transparent material. Theelectrodes 13, 14 may be applied to such mounting material and theencapsulated liquid crystal material/emulsion, including many capsules11, for example, may be sandwiched between such mounting material 12a,12b to form the apparatus 10, as will be described in further detailbelow.

A reflectance medium 18 forms an interface 19 with the lower supportmedium portion 12b to obtain the desired total internal reflectionfunction, which will be described in greater detail below. Suffice it tosay here, though, that due to the total internal reflection princple ofoperation, the liquid crystal material in the capsule 11 will beilluminated by incident light, for example represented by a light beam17, and with light that it isotropically scatters in the apparatus 10 sothat from the viewing area 20 beyond the upper support medium portion12a, the liquid crystal material 11 will appear colored and relativelybright when under a no-field condition, e.g. the switch 15 is open.Although such isotropic scattering (and some absorption, especially witha pleochroic dye present in the encapsulated liquid crystal material)occurs in applicant's invention disclosed in the above co-pendingapplication Ser. No. 302,780, the total internal reflection principle ofthe present invention enhances scattering and coloring of thereflected/scattered light by the non-pleochroic dye and, thus, brightensthe visual/optical colored appearance of characters etc., formed oroutput by the encapsulated liquid crystal material. A light absorbinglayer 21 of black or colored material may be applied to the bottom orback surface of the reflectance medium 18 remote from the interface 19to absorb light incident on the layer 21.

The electrode 13 may be, for example, a quantity of vacuum depositedindium tin oxide applied to the lower support medium portion 12b, andthe electrode 14 may be, for example, electrically conductive inkapplied directly to the liquid crystal material or could be like theelectrode 13. Other electrode material and mounting means therefore alsomay be used for either electrode. Examples include tin oxide andantimony doped tin oxide. Preferably the electrodes are relatively thin,for example, about 200 angstroms thick, and transparent so that they donot significantly affect the optics of the liquid crystal apparatus 10.

The encapsulated liquid crystal material 11 includes liquid crystal 30contained within the confines of interior volume 31 of a capsule 32.Each capsule 32 may be a discrete one or alternatively the liquidcrystal 30 may be contained in a stable emulsion of a containment mediumor so-called encapsulating material 33 that tends to form a multitude ofcapsule-like environments for containing the liquid crystal material.For convenience of illustration, the capsules 32 are shown as discretecapsules in and preferably formed of the overall quantity of containmentmedium or encapsulating material 33. According to the preferredembodiment and best mode of the present invention, the capsule 32 isgenerally spherical, and the liquid crystal 30 is nematic oroperationally nematic liquid crystal material having positive dielectricanisotropy. However, the principles of the invention would apply whenthe capsule 32 is of a shape other than spherical; such shape shouldprovide the desired optical and electrical characteristics that willsatisfactorily coact with the optical characteristics of the liquidcrystal material 30, e.g. index of refraction, and will permit anadequate portion of the electric field to occur across the liquidcrystal 30 itself for effecting desired ordered or parallel alignment ofthe liquid crystal when it is desired to have a field-on condition. Theshape also should tend to distort the liquid crystal material when in afield-off or random alignment condition. A particular advantage to thepreferred spherical configuration of the capsule 32 is the distortion iteffects on the liquid crystal 30 therein when in a field-off condition.This distortion is due, at least in part, to the relative sizes of thecapsules and the pitch of the liquid crystal; they preferably are aboutthe same or at least about the same order of magnitude. Moreover,nematic liquid crystal material has fluid-like properties thatfacilitate the conformance or the distortion thereof to the shape of thecapsule wall in the absence of an electric field. On the other hand, inthe presence of an electric field such nematic material will relativelyeasily change to ordered alignment with respect to such field.

Liquid crystal material of a type other than nematic or combinations ofvarious types of liquid crystal material and/or other additives may beused with or substituted for the preferred nematic liquid crystalmaterial as long as the encapsulated liquid crystal is operationallynematic. However, cholesteric and smectic liquid crystal materialgenerally are bulk drive. It is more difficult to break up the bulkstructure thereof for conformance to capsule wall shape and energyconsiderations in the capsule.

Dye 9 may be directly in the containment medium 33 itself. the quantityof dye may be as small as about 0.01% to about 1% by weight of thecontainment medium 33 and preferably from about 0.1% to about 0.5%.Preferably the containment medium is water base and the dye is watersoluble. Therefore, the dye will dissolve therein and will not migrateto the liquid crystal. However, due to the long path length of most ofthe light in the containment medium, such small quantity of dye willhave an effective light coloring result. Moreover, it has beendiscovered that the light coloring of the present invention results inthe appearance of pigmented colors, such as a pigmented green, e.g. likegreen paint, this is in distinction to the relatively poor quality ofgreen light, for example, obtained using a green dyed filter. Similarexperiences occur for other colors, too.

Exemplary non-pleochroic dyes include water soluble dyes, food coloringdyes, and cloth or fabric dyes. Particular examples include FD&C Blue #2indigo carmine, FD&C Red #2 amaranth, FD&C Red #3 erythorsine, FD&CYellow #5 tartazine, as well as, from American Color Corp. Direct Orange72, Direct Red 80, Direct Red 81, Direct Blue I, Direct Yellow #4GL, anddirect Yellow #6.

Alternatively, the dye 9 may be an oil soluble dye which dissolves inthe oil base liquid crystal material and does not migrate to thecontainment medium. Examples of such dyes include: FD&C Yellow #2,Naphthol Yellow S.

Turning to FIGS. 2 and 3, a schematic representation of the singlecapsule 32 containing liquid crystal 30 is shown, respectively, in thefield-off and field-on conditions. The capsules 32 are spherical andhave a generally smooth curved interior wall surface 50 defining theboundary for the volume 31. The actual dimensional parameters of thewall surface 50 and of the overall capsule 32 are related to thequantity of liquid crystal 30 contained therein and possibly to othercharacteristics of the individual liquid crystal material therein.Additionally, the capsule 32 applies a force to the liquid crystals 30tending to pressurize or at least to maintain substantially constant thepressure within the volume 31. As a result of the foregoing, and due tothe surface wetting nature of the liquid crystal, the liquid crystalwhich ordinarily in free form would tend to be parallel, althoughperhaps randomly distributed, are distorted to curve in a direction thatgenerally is parallel to a relatively proximate portion of the interiorwall surface 50. Due to such distortion the liquid crystals storeelastic energy. For simplicity of illustration, a layer 51 of liquidcrystal molecules whose directional orientation is represented byrespective dashed lines 52 is shown in closest proximity to the interiorwall surface 50. The directional orientation of the liquid crystalmolecules 52 is distorted to curve in the direction that is parallel toa proximate area of the wall surface 50. The directional pattern of theliquid crystal molecules away from the boundary layer 52 within thecapsule is represented by 53. The liquid crystal molecules aredirectionally represented in layers, but it will be appreciated that themolecules themselves are not confined to such layers. Thus, theorganization in an individual capsule is predetermined by theorganization of the structure 52 at the wall and is fixed unless actedon by outside forces, e.g. an electric field. On removal of the electricfield the directional orientation would revert back to the original one,such as that shown in FIG. 2.

Nematic type material usually assumes a parallel configuration andusually is optical polarization direction sensitive. However, since thematerial 52 in the encapsulated liquid crystal 11 is distorted or forcedto curved form in the full three dimensions of the capsule 32, suchnematic liquid crystal material in such capsule takes on an improvedcharacteristic of being insensitive to the direction of opticalpolarization of incident light.

The liquid crystal 30 in the capsule 32 has a discontinuity 55 in thegenerally spherical orientation thereof due to the inability of theliquid crystal to align uniformly in a manner compatible with parallelalignment with the wall 50 and a requirement for minimum elastic energy.Such discontinuity is in three dimensions and is useful to effect adistorting of the liquid crystal 30 further to decrease the possibilitythat the liquid crystal 30 would be sensitive to optical polarizationdirection of incident light. The discontinuity protrusion 55 would tendto cause scattering and absorption within the capsule, and thetangential or parallel alignment of the liquid crystal molecules withrespect to portions of the interior wall surface 50 of the capsules bothcause scattering and absorption within the capsule 32. When the electricfield is applied, for example, as is shown in FIG. 3, the discontinuitywill no longer exist so that such discontinuity will have a minimumeffect on optical transmission when the encapsulated liquid crystal 11is in a field-on or aligned condition.

Although the foregoing discussion has been in terms of a homogeneousorientation of the liquid crystal material (parallel to the capsulewall), such is not a requisite of the invention. All that is required isthat the interaction between the wall and the liquid crystal product anorientation in the liquid crystal near that wall that is generallyuniform and piecewise continuous, so that the spatial averageorientation of the liquid crystal material over the capsule volume isstrongly curved and there is no substantial parallel direction oforientation of the liquid crystal structure in the absence of anelectric field. It is this strongly curved orientation that results inthe scattering and polarization insensitivity in the field-offcondition, which is a feature of this invention.

In the field-on condition, or any other condition which results in theliquid crystal being in ordered or parallel alignment, as is shown inFIG. 3, the encapsulated liquid crystal 11 will transmit substantiallyall the light incident thereon and will tend not to be visible in thesupport medium 12. On the other hand, in the field-off condition whenthe liquid crystal is in distorted alignment, sometimes referred toherein as random alignment, for example as is shown in FIG. 2, some ofthe incident light will be absorbed, but also some of the incident lightwill tend to be scattered isotropically in the support medium 12. Usingtotal internal reflection such isotropically scattered light can beredirected to the, for example dyed, encapsulated liquid crystal 11 thusbrigtening the same tending to cause it to appear colored and relativelybright to a viewer or viewing instrument.

The index of refraction of the encapsulating medium 32 and the ordinaryindex of refraction of the liquid crystal 30 should be matched as muchas possible when in the field-on or liquid crystal orderly alignedcondition to avoid optical distortion due to refraction of incidentlight passing therethrough. However, when the liquid crystal material isin distorted or random alignment, i.e. there is no field applied, therewill be a difference in the indices of refraction at the bounary of theliquid crystal 30 and wall of capsule 32; the extraordinary index ofrefraction of the liquid crystal is greater than the index of refractionof the encapsulating medium. This causes refraction at the interface orboundary of the liquid crystal material and of the containment orencapsulating medium and, thus, further scattering. Light that is sofurther scattered will be internally reflected for further brighteningin the liquid crystal appearance. Such occurrence of different indicesof refraction is known as birefringence. Principles of birefringence aredescribed in Optics by Sears and in Crystals And The PolarizingMicroscope by Hartshorne and Stewart, the relevant disclosures of whichare hereby incorporated by reference. Preferably the encapsulating orcontainment medium 32 and the support medium 12 have the same index ofrefraction to appear optically substantially as the same material, thusavoiding a further optical interface.

As long as the ordinary index of refraction of the liquid crystalmaterial is closer to the index of refraction of the so-calledencapsulating medium, than is the extraordinary index of refraction, achange in scattering will result when going from field-on to field-offconditions, and vice-versa. Maximum contrast results when the ordinaryindex of refraction matches the index of refraction of the medium. Thecloseness of the index matching will be dependent on the desired degreeof contrast and transparency in the device, but the ordinary index ofrefraction of the crystal and the index of the medium will preferablydiffer by no more than 0.03, more preferably 0.01, especially 0.001. Thetolerated difference will depend upon capsule size.

According to the preferred embodiment and best mode, desirably theelectric field E shown on FIG. 3 is applied to the liquid crystal 30 inthe capsule 32 for the most part rather than being dissipated or droppedsubstantially in the encapsulating material. There should not be asubstantial voltage drop across or through the material of which thewall 54 of the capsule 32 is formed; rather, the voltage drop shouldoccur across the liquid crystal 30 within the volume 31 of the capsule32.

The electrical impedance of the encapsulating medium preferably shouldin effect be large enough relative to that of the liquid crystal in theencapsulated liquid crystal 11 that a short circuit will not occurexclusively through the wall 54, say from point A via only the wall topoint B, bypassing the liquid crystal. Therefore, for example, theeffective impedance to induced or displacement current flow through orvia only the wall 54 from point A to point B should be greater than theimpedance that would be encountered in a path from point A to point A'inside the interior wall surface 50, through the liquid crystal material30 to point B' still within the volume 31, ultimately to point B again.This condition will assure that there will be a potential differencebetween point A and point B. Such potential difference should be largeenough to produce an electric field across the liquid crystal materialthat will tend to align the same. It will be appreciated that due togeometrical considerations, namely the length through only the wall frompoint A to point B, for example, such condition still can be met eventhough the actual impedance of the wall material is lower than that ofthe liquid crystal material therein.

The dielectric constants (coefficients) of the material of which theencapsulating medium is formed and of which the liquid crystal iscomprised, and the effective capacitance values of the capsule wall 54,particularly in a radial direction and of the liquid crystal acrosswhich the electric field E is imposed, all should be so related that thewall 54 of the capsule 32 does not substantially drop the magnitude ofthe applied electric field E. Ideally the capacitance dielectricconstants (coefficients) of the entire layer 61 (FIG. 4) of encapsulatedliquid crystal material should be substantially the same for thefield-on condition.

The liquid crystal 30 will have a dielectric constant value that isanisotropic. It is preferably that the dielectric constant (coefficient)of the wall 54 be no lower than the dielectric constant (coefficient) ofthe anisotropic liquid crystal material 30 to help meet the aboveconditions for optimum operation. It is desirable to have a relativelyhigh positive dielectric anisotropy in order to reduce the voltagerequirements for the electric field E. The differential between thedielectric constant (coefficient) for the liquid crystal 30 when noelectric field is applied, which should be rather small, and thedielectric constant (coefficient) for the liquid crystal when it isaligned upon application of an electric field, which should berelatively large, should be as large as possible. The dielectricconstants (coefficients) relationships are discussed in the concurrentlyfiled application, the entire disclosure of which is specificallyincorporated by reference here. It should be noted, in particular,though, that the critical relationship of dielectric values and appliedelectric field should be such that the field applied across the liquidcrystal material in the capsule(s) is adequate to cause alignment of theliquid cyrstal structure with respect to the field. The lower dielectricvalues of commonly used liquid crystals are, for example, from as low asabout 3.5 to as high as about 8.

The capsules 32 may be of various sizes. The smaller the size, though,the higher the requirements will be for the electric field to effectalignment of the liquid crystal in the capsule. Preferably, though, thecapsules should be of uniform size parameters so that the variouscharacteristics, such as the optical and electrical characteristics, ofan apparatus, such as a display, using the encapsulated liquid crystalwill be substantially uniform. Moreover, the capsules 32 should be atleast 1 micron in diameter so they appear as discrete capsules relativeto an incident light beam; a smaller diameter would result in the lightbeam "seeing" the capsules as a continuous homogeneous layer and wouldnot undergo the required isotropic scattering. Examples of capsulesizes, say from 1-30 microns diameter, and of liquid crystal materialare in the above concurrently filed application and are herebyspecifically incorporated by reference.

A preferred liquid crystal material in accordance with the best mode ofthe invention is that nematic material NM-8250, an ester sold byAmerican Liquid Xtal Chemical Corp., Kent, Ohio, U.S.A. Other examplesmay be ester combinations, biphenyl and/or biphenyl combinations, andthe like.

Several other types of liquid crystal material useful according to theinvention include the following four examples, each being a recipe forthe respective liquid crystal materials. The so-called 10% material hasabout 10% 4-cyano substituted materials; the 20% material has about 20%4-cyano substituted materials, and so on.

    ______________________________________                                        10% Material                                                                  Pentylphenylmethoxy Benzoate                                                                       54       grams                                           Pentylphenylpentyloxy Benzoate                                                                     36       grams                                           Cyanophenylpentyl Benzoate                                                                         2.6      grams                                           Cyanophenylheptyl Benzoate                                                                         3.9      grams                                           Cyanophenylpentyloxy Benzoate                                                                      1.2      grams                                           Cyanophenylheptyloxy Benzoate                                                                      1.1      grams                                           Cyanophenyloctyloxy Benzoate                                                                       9.94     grams                                           Cyanophenylmethoxy Benzoate                                                                        0.35     grams                                           20% Material                                                                  Pentylphenylmethoxy Benzoate                                                                       48       grams                                           Pentylphenylpentyloxy Benzoate                                                                     32       grams                                           Cyanophenylpentyl Benzoate                                                                         5.17     grams                                           Cyanophenylheptyl Benzoate                                                                         7.75     grams                                           Cyanophenylpentyloxy Benzoate                                                                      2.35     grams                                           Cyanophenylheptyloxy Benzoate                                                                      2.12     grams                                           Cyanophenyloctyloxy Benzoate                                                                       1.88     grams                                           Cyanophenylmethoxy Benzoate                                                                        0.705    grams                                           40% Material                                                                  Pentylphenylmethoxy Benzoate                                                                       36       grams                                           Pentylphenylpentyloxy Benzoate                                                                     24       grams                                           Cyanophenylpentyl Benzoate                                                                         10.35    grams                                           Cyanophenylheptyl Benzoate                                                                         15.52    grams                                           Cyanophenylpentyloxy Benozate                                                                      4.7      grams                                           Cyanophenylheptyloxy Benzoate                                                                      4.23     grams                                           Cyanophenyloctyloxy Benzoate                                                                       3.76     grams                                           Cyanophenylmethoxy Benzoate                                                                        1.41     grams                                           40% MOD                                                                       Pentylphenylmethoxy Benzoate                                                                       36       grams                                           Pentylphenylpentyloxy Benzoate                                                                     24       grams                                           Cyanophenylpentyl Benzoate                                                                         16       grams                                           Cyanophenylheptyl Benzoate                                                                         24       grams                                           ______________________________________                                    

The encapsulating medium forming respective capsules 32 should be of atype that is substantially completely unaffected by and does not affectthe liquid crystal material. Various resins and/or polymers may be usedas the encapsulating medium. A preferred encapsulating medium ispolyvinyl alcohol (PVA), which has a good, relatively high, dielectricconstant and an index of refraction that is relatively closely matchedto that of the preferred liquid crystal material. An example ofpreferred PVA is an about 84% hydrolized, molecular weight of at leastabout 1,000 resin. Use of a PVA of Monsanto Company identified asGelvatol 20/30 represents the best mode of the invention.

A method for making emulsified or encapsulated liquid crystals 11 mayinclude mixing together the containment or encapsulating medium, theliquid crystal material, and perhaps a carrier medium, such as water.Mixing may occur in a variety of mixer devices, such as a blender, acolloid mil, which is most preferred, or the like. What occurs duringsuch mixing is the formation of an emulsion of the ingredients, whichsubsequently can be dried eliminating the carrier medium, such as water,and satisfactorily curing the encapsulating medium, such as the PVA.Although the capsule 32 of each thusly made encapsulated liquid crystal11 may not be a perfect sphere, each capsule will be substantiallyspherical in configuration because a sphere is the lowest free energystate of the individual droplets, globules or capsules of the emulsion,both when originally formed and after drying and/or curing. Moreover, ifthe dye used is a water soluble one, it should be pre-mixed and/ordissolved in the water base material or medium, such as the PVAcontainment medium; and if the dye is oil soluble, then it should bepre-mixed and/or dissolved in the oil base component, such as the liquidcrystal material.

The capsule size (diameter) preferably should be uniform in the emulsionfor uniformity of operation with respect to effect on incident light andresponse to electric field. Exemplary capsule size range may be fromabout 0.3 to about 100 microns, preferably 0.3 to 30 microns, especially3 to 15 microns, for example 5 to 15 microns.

Various techniques may be employed to form the support medium 12, whichmay be of the same or similar material as the encapsulating orcontainment medium. For example, the lower support medium 12b may beformed using a molding or casting process. The electrode 13 and liquidcrystal material may be applied for support by that medium 12b. Theelectrode may be a layer of Intrex material between the support mediumand the encapsulated liquid crystal material. The electrode 14 may beapplied, e.g. by printing. Thereafter, the upper support medium portion12a may be poured or cast in place to complete enclosing theencapsulated liquid crystal material and the electrodes. Alternatively,the support medium portions 12a, 12b may be a substantially transparentplastic-like film or a plate of glass, as is described in Example 1, forexample. Most preferably the support medium portions 12a and 12b are apolyester film, such as Mylar.

The reflectance medium 18, if a solid, for example, may be applied tothe support medium portion 12b by a further casting or moldingtechnique, and a lower coating 21 of black or colored light absorbingmaterial may be applied to the back surface of the reflectance medium18, i.e. the surface remote from the interface thereof with the lowersupport medium portion 12b. Alternatively, the reflectance medium may bean air or other fluid gap between the support medium portion 12b and theabsorber 21, or a tuned dielectric layer may be applied by conventionalevaporation technique directly to the bottom surface of the lowersupport medium portion 12b in place of the reflectance medium 18, aswill be described further below.

The following is an example of materials and one method for makingliquid crystal display devices and operational characteristics thereofin accordance with the present invention.

EXAMPLE 1

An example of dyed isotropically scattering material was made using 15grams of 22% (the other 78% was water) solution of low viscosity mediumhydrolysis polymer (Gelvatol polyvinyl alcohol - PVA), 5 grams of theabove 40% recipe liquid crystal material, 3% cholesteryl oleate, 0.1% LO630 1% solution (i.e. the amount of the LO 630 was about 0.1% of theweight of the liquid crystal material), 15% chloroform (0.75 grams), and0.4% (i.e. 0.06 grams) of M. C. Green liquid dye.

The dye was dissolved in the PVA and then all the above ingredients werecombined. The mixture was passed through a screen filtering system onlow vacuum insert screens CBB and AA which filtered the material veryslowly into a small filtering flask.

A slide was made of the filtered emulsified material. On observationthrough a microscope after the material has dried the capsules weremeasured at about 3 to 4 microns diameter.

A film of such emulsified material was pulled using a doctor blade at agap 5 setting on an Intrex electrode mounted on a clear Mylar filmsupport. The emulsion film was allowed to dry. In operation the stableemulsion film scattered light in the absence of electric field, began totransmit light (i.e. to align the liquid crystal structure with respectto an electric field) at a voltage of about 10 volts, and was full on(transmitting) at about 30 volts.

EXAMPLE 2

The ingredients and method of Example 1 were followed except a 0.4% ofM. C. Blue liquid dye was substituted for the Green dye. The resultswere the same.

To improve the emulsion stability and coating uniformity the GAFCorporation LO 630 non-ionic surfactant (detergent) was added before themixing step. Improved performance in stability of the emulsion and incoating of the emulsion onto the electrode/polyester film base werenoted.

Thus, it will be appreciated that in accordance with the invention asurfactant, preferably a non-ionic surfactant, a detergent, or the likemay be mixed with the encapsulated liquid crystal material prior todepositing on the electrode coated film, as was just described above.

The chiral additive (cholesteryl oleate) noted in the examples aboveimproved (reduced) the response time of the operationally nematicencapsulated liquid crystal material, particularly in returning to thedistorted alignment generally following the wall shape of the individualcapsules, promptly after going from a field on to a field off condition.In relatively large capsules, say about on the order of at least 8microns total diameter, when going to the field off condition, it is theusual case that the liquid crystal material adjacent the capsule wallwould return to the distorted alignment following the capsule wall shapeor curvature faster than would the liquid crystal material closer to thecenter of the capsule; this disparity tends to slow the overall responsetime of the material. However, the chiral additive induces a tendencyfor the structure to twist. This influences on the nematic material ismost noticeable remote from the capsule wall and, thus, speeds up thereturn of such relatively remote material to distorted alignment,preferably influenced by the shape of the capsule wall. Such chiraladditive may be in the range of about 0.1% to about 8% of the liquidcrystal material and a preferred range of about 2% to about 5%. Theamount may vary depending on the additive and the liquid crystal andcould even be outside the stated range as long as the capsule remainsoperationally nematic.

Another additive, namely the chloroform, noted in the above examplesalso may be used to reduce and/or otherwise to control the viscosity ofthe liquid crystal during manufacturing of a device 60, for example. Thereduced viscosity may have a positive effect on emulsion formationand/or on the process of applying the emulsion to an electrode coveredsupport medium 12. The chloroform, which is water-soluble, leaves theemulsion on drying.

In accordance with the invention, other types of support media 12 thatmay be used include polyester materials; and polycarbonate material,such as Kodel film. Tedlar film, which is very inert, also may be usedif adequate adhesion of the electrode can be accomplished. Such media 12preferably should be substantially optically transparent.

Another example of an acid type containment medium useful in theinvention is carbopole (carboxy polymethylene polymer by B. F. GoodrichChemical Company), or polyacid.

In accordance with the invention, several other polymer containmentmedia that may be used are listed in Chart I below. The chart alsoindicates several characteristics of the respective polymers.

    __________________________________________________________________________    CHART I                                                                                                      Temperature                                                             Molecular                                                                           &                                              Containment Medium                                                                       Viscosity                                                                           % Hydrolyzed                                                                          Weight                                                                              % Solutions                                    __________________________________________________________________________    20/30      4-6 CPS                                                                             88.7-85.5                                                                             10,000                                                                              4% at 20° C.                            Gelvatol, by                                                                  Monsanto Company                                                              40/20      2.4-3 CPS                                                                             77-72.9                                                                              3,000                                                                              4% at 20° C.                            Gelvatol, by                                                                  Monsanto Company                                                              523, by    21-25 87-89   --    4% at 20° C.                            Air Products And                                                              Chemicals, Inc.                                                               72/60      55-60  99-100 --    4% at 20° C.                            Elvanol, by                                                                   DuPont Co.                                                                    405        2-4 CPS                                                                             80-82   --    4% at 20° C.                            Poval, by                                                                     Kurashiki                                                                     __________________________________________________________________________

Other Gelvatol PVA materials that may be used include those designatedby Monsanto as 20-90; 9000; 20-60; 6000; 3000; and 40-10.

A preferred quantity ratio of liquid crystal material to containmentmedium is about one part by weight liquid crystal material to aboutthree parts by weight of containment medium. Acceptable encapsulatedliquid crystal emulsion operative according to the invention also may beachieved using a quantity ratio of about one part liquid crystalmaterial to about two parts containment medium, e.g., Gelvatol PVA.Moreover, although a 1:1 ratio also will work, generally it will notfunction quite as well as material in the ratio range of from about 1:2to about 1:3.

Turning now to FIGS. 4 and 5, a portion 60 of a liquid crystal displaydevice in accordance with the present invention is illustrated. Theportion or device 60 is a completion of the liquid crystal apparatus 10described above with reference to FIG. 1 in that plural encapsulatedliquid crystals 11, indeed plural layers thereof, are contained in asupport medium 12. The sizes, thicknesses, diameters, etc., of theseveral parts shown in FIGS. 4 and 5 are not necessarily to scale;rather the sizes are such as is necessary to illustrate the severalparts and their operation, as is described below, in accordance with theinvention.

The electrodes 13, 14 are employed to apply a desired electric field toeffect selective alignment of the liquid crystal material in the mannershown in FIG. 3, for example. Means other than electrodes may beemployed to apply some type of input to the display device 60 for thepurpose of effecting ordered or random alignment of the liquid crystal.

The encapsulated liquid crystals 11 are arranged in several layers 61within the display portion 60. The layers 61 may be divided into severalportions representing the various characters or portions of charactersintended to be displayed by the display 60. For example, the longerlefthand portion 61L of the layers 61 shown in FIG. 4 may represent asection view through one part of a well known 7-segment display pattern,and the relatively short righthand portion 61R of the layers 61 shown inFIG. 4 may represent a part of another 7-segment character display. Itwill be appreciated, though, that various patterns of liquid crystalmaterial may be employed in accordance with the present invention. Azone 62 of support medium 12 fills the area between the liquid crystallayer portions 61L, 61R. Subsequent reference to layers 61 will be inthe collective, i.e. referring to layer 61 as including the severallevels or layers comprising the same. As an example, the compositethickness of such layer 61 may be from about 0.3 mils to about 10 mils;uniform thickness is preferred for uniform response to electric field,scattering, etc.

It is significant to note that such an arrangement or pattern ofencapsulated liquid crystal material layer portions, such as at 61L and61R, separated at zone 62 by support medium 12 or other material isfacilitated, or even made possible due to the encapsulating or confiningof the liquid crystal in discrete containment media, such as is formedby the preferred stable emulsion. Therefore, especially on a relativelylarge size device such as a display, billboard, optical shutter, etc.,encapsulated liquid crystal material may be applied to the supportmedium 12 only where it is required to provide the selectable opticalcharacteristics. Such patterning of the encapsulated liquid crystalmaterial can in some instances, then, appreciably reduce the amount ofsuch material required for a particular application. Such patterning isfurther made possible consistent with desired operation of a deviceusing encapsulated liquid crystal material in accordance with theinvention due to the functional operation thereof as will be describedin detail below.

The display 60 may be used, for example, in an air environment, such airbeing represented by the reference numeral 63, and the air forms aninterface 64 at the viewing side or from the viewing direction 20 withthe support medium 12. The index of refraction N of the external medium63 is different from the index of refraction N' of the encapsulatingmedium 12, the latter usually being larger than the former. As a result,a beam of light 65, which arrives generally from the viewing direction20, passing through the interface 64 into the support medium 12 will bebent toward the normal, which is an imaginary line 66 perpendicular tothat interface 64. That light beam 65a inside the support medium 12 willbe closer to normal than the incident beam 65 satisfying the equationrelationship N Sine θ=N' Sine θ', wherein θ is the angle of the incidentlight beam 65 with respect to the normal and θ' is the angle of thelight beam 65a with respect to normal. Such mathematical relationshipwill apply at the interface 19, as follows: N' Sine θ=N" Sine θ". Toachieve the desired total internal reflection in accordance with theinvention, the index of refraction N" of the reflectance medium 18 issmaller than the index of refraction N' of the support medium 12.Accordingly, if the light beam 65a, for example, were able to and didpass through the interface 19, it would be bent away from the normal atthe interface 19 to the angle θ" with respect to normal. Actually, sincethe light beam 65, 65a is not scattered off course by the liquid crystalmaterial in layers 61, i.e., because it passes through the zone 62, itwill indeed likely exit through the interface 19.

Continuing to refer particularly to FIG. 4, operation of a liquidcrystal display 60 in accordance with the invention is now described.The operationally nematic liquid crystal 30 is in distorted or randomalignment due to existence of a field-off condition. Incident light beam70 enters the support medium 12 at the interface 64 and is bent as thelight 70a that impinges as incident light on the layer 61 ofencapsulated liquid crystal. The random or distorted encapsulated liquidcrystal material will isotropically scatter the light incident thereon.Therefore, there are several possibilities of how such incident lightbeam 70a would tend to be scattered, as follows:

A. For example, one possibility is that the incident light beam 70a willbe directed according to the dotted line 70b toward the interface 19.The angle at which the light beam 70b impinges on the interface 19 iswithin the illustrated solid angle α (defined in the planar direction ofthe drawing of FIG. 4 by the dashed lines 71) of a so-called cone ofillumination. Light falling within such solid angle α or cone ofillumination is at too small an angle with respect to normal at theinterface 19 to be totally internally reflected at that interface;therefore, the light beam 70b will pass through interface 19 whilebending away from the normal to form the light beam 70c. Light beam 70cpasses into the reflectance medium 18 and is absorbed by layer 21.

B. Another possibility is that the light beam 70a will be isotropicallyscattered in the direction of the light beam 70d outside the cone angleα. Total internal reflection will occur at the interface 19 causing thelight beam 70d to be reflected as light beam 70e back to the layer 61 ofencapsulated liquid crystal material where it will be treated as anotherindependently incident light beam thereto, just like the light beam 70afrom which it was derived. Therefor, such light beam 70e will undergoisotropic scattering again as is described herein.

C. Still another possibility is that the incident light beam 70a, orthat derived therefrom, such as the light beam 70e, will beisotropically scattered toward the interface 64 at an angle that is soclose to normal at that interface 64 that the light beam will passthrough the interface 64 into the "medium" 63, such as the air, to beviewed by an observer or observing instrument. The solid angle α' of acone of illumination, like the cone angle α mentioned above, withinwhich such scattered light beam 70e must fall to be emitted out throughthe interface 64 is represented by the single dot phantom lines 72.Light beam 70f represents such a light beam that is so emitted from thedisplay 60. It is that light, e.g. the sum of such emitted light beams70f, which exits at the interface 64 that causes the layer 61 ofencapsulated liquid crystals 11 to give the appearance of a coloredbright character as viewed from the viewing direction 20.

D. Still a further possibility is that the light beam 70a may beisotropically scattered in the direction of the light beam 70g. Lightbeam 70g is outside the solid cone angle α' and, therefore, will undergototal internal reflection at the interface 64, whereupon the reflectedbeam 70h will impinge back on the layer 61 as an effectively independentincident light beam, like the beam 70e mentioned above and having asimilar effect.

The index of refraction of the electrodes 13,14 usually will be higherthan that (those) of the containment medium and support medium and thecontainment and support media indices of refraction preferably are atleast about the same. Therefore, the light passing from the containmentmedium into the electrode material will bend toward the normal, and thatpassing from the electrode into the support medium will bend away fromthe normal; the net effect of the electrode thus being nil orsubstantially negligible. Accordingly, the majority of total internalreflection will occur at the interfaces 19,64.

As viewed from the viewing direction 20, the zone 62 will appear dark orcolored according to the composition of the absorbent layer 21. This isdue to the fact that the light beam 65, 65a, 65b, representing themajority of light that passes through zone 62, will tend to pass throughinterface 64, support medium 12, the interface 19 and the reflectancemedium 18, being bent toward or away from the normal, at respectiveinterfaces as shown, ultimately being substantially absorbed by layer21.

Briefly referring to FIG. 5, the field-on ordered alignment conditionand operation of the encapsulated liquid crystal layer 61 in the displaydevice 60 are shown. The encapsulated liquid crystal 11 in the layer 61of FIG. 5 are like those seen in FIG. 3. Therefore, like the light beam65, 65a, 65b which passes through the zone 62 and is absorbed by thelayer 21, the light beam 70, 70a, 70i will follow a similar path alsobeing transmitted through the aligned and, thus, effectively transparentor non-scattering layer 61. At the interface 19, the light beam 70a willbe bent away from the normal and subsequently light beam 70i will beabsorbed by the layer 21. Accordingly, whatever visual appearance thelight beam 65 would tend to cause with respect to an observer at theviewing location 20, so too will the light beam 70 cause the same effectwhen passing through the orderly aligned encapsulated liquid crystalmaterial. Thus, when the display 60, and particularly the encapsulatedliquid crystal material therein, is in the orderly aligned or field-oncondition, the area at which the liquid crystal is located will havesubstantially the same appearance as that of the zone 62.

It is noted that if either the incident beam 65 or 70 were to enter thesupport medium 12 at the interface 64 at such a large angle with respectto the normal there, and, therefore, ultimately to impinge on theinterface 19 at an angle greater than one falling within the so-calledcone of light angle α, such beam would be totally internally reflectedat the interface 19. However, such reflected light probably would remainwithin the support medium 12 due to subsequent transmission through thelayer of liquid crystal material 61 and subsequent total internalreflectance at the interface 64, etc.

In FIG. 6, the preferred reflectance medium 80 air is illustrated. InFIG. 6 primed reference numerals designate elements corresponding tothose designated by the same umprimed reference numerals in FIGS. 4 and5. The display 60' has an interface 19' formed with air 80. To achieveabsorbence of the light transmitted through the interface 19' and medium80, a black or colored absorber 81 may be positioned at a locationdisplaced from the interface 19'. The preferred absorber 81 is carbonblack which may be mounted on a support surface positioned generally asis shown in FIG. 6. The preferred liquid crystal is NM-8250 and thepreferred containment medium is PVA, as are mentioned above; and thepreferred support medium 12 is polyester. Moreover, it is preferred thatthe index of refraction of the support medium 12a, 12b, for example, andthat of the containment medium for the liquid crystal be at leastsubstantially the same; this helps to assure that the total internalreflection will occur primarily at the interfaces 19', 64' and not verymuch, if at all, at the interface between the containment medium andsupport medium; this minimizes optical distortion while maximizingcontrast. The display 60' functions substantially the same as thedisplay 60 described above with reference to FIGS. 4 and 5.

Referring, now, to FIGS. 7 and 8, a modified liquid crystal display 90is illustrated. The liquid crystal display 90 includes a support medium12 with a layer of encapsulated liquid crystal material 61, as above.However, at the interface 19 there is a tuned dielectric interferencelayer 91. The thickness of the dielectric layer 91, which is exaggeratedin the drawings, preferably is an odd whole number function or multipleof lambda divided by two such as 3λ/2, 5λ/2, etc., wherein λ is thewavelength of the light in the support display 60. The tuned dielectricinterference layer 91 may be applied to the back surface of the supportmedium 12 by conventional evaporation technique. Such dielectric layermay be comprised of barium oxide (BaO), lithium fluoride (LiF) or othermaterial that provides the desired optical interference function.Preferably such layer has a smaller index of refraction than the medium12 to obtain an interface 19 at which total internal reflection of lightwithin cone angle α will be internally reflected. A comprehensivedescription of optical interference is found in Optics by Born and Wolf,Fundamentals of Physics, 2nd Ed., 1981, Resnick and Halliday, pgs.731-735, and in University Physics by Sears and Zemansky, the relevantdisclosures of which are hereby incorporated by reference.

In the field-off/random liquid crystal alignemnt condition shown in FIG.7 the display 90 will function substantially the same as the display 60described above with respect to: (a) isotropic scattering of light bythe encapsulated liquid crystal material layer 61; (b) the totalinternal reflection of that light falling outside the solid angle coneα, this due to the interface 19 seen in FIG. 7, (or α' with respect tolight isotropically scattered to the interface 64), and; (c) thetransmitting of light, such as the light beam 70f, toward the viewingdirection 20 to give the appearance of a white character on a relativelydark background.

By use of the tuned dielectric interference layer 91 and opticalinterference, in the field-off condition the illumination effected ofthe encapsulated liquid crystal layer 61 is further enhanced.Specifically, the effective cone of light angle α becomes reduced to theangle φ shown in FIG. 7. Generally, an incident light beam 92 impingingon the interface 64 will be deflected as the light beam 92a which thenis incident on the layer 61. If the light beam 92a were isotropicallyscattered as beam 92b at an angle outside the original angle α, thetotal internal reflection operation described above with reference tothe display 60 will occur. However, if the light beam 92a isisotropically scattered as light beam 92c at an angle falling within thecone of light α but outside the cone of light φ, it will actually bereflected constructive optical interference will occur further toenhance the illumination of the encapsulated liquid crystal layer 61.

More particularly when the light beam 92c enters the tuned dielectricinterference layer 91, at least a portion 92d actually will be reflectedback toward the interface 19. At the interface 19, there will beconstructive interference with another incident light beam 93 increasingthe effective intensity of the internally reflected resultant light beam94, which is directed back toward the encapsulated liquid crystal layer61 enhancing the illumination thereof. The result of such constructiveinterference is that the display 90 yields more light beams scattered upto or reflected up to the layer 61 than in the display 60. However,there is a disadvantage in that the viewing angle at which the display90 will function effectively is less than the viewing angle at which thedisplay 60 will function effectively. Specifically, incident lightentering the support medium 12 at an angle equal or less than the angleδ with respect to the interface 64, will tend to be totally reflectedbecause the back or reflective surface of the tuned dielectricinterference layer 91 will tend to act as a mirror so that some contrastwill be lost in the display 90. The angle δ, if it exists at all, inconnection with the display 60 would tend to be smaller than the angleof the display 90.

Light beams 95 and 96 (FIG. 7) that pass through the zone 62 of thedisplay 90 and light beams 92' (FIG. 8) that pass through the orderlyaligned (field-on) liquid crystal layer 61 and fall within the coneangle O will undergo destructive optical inteference. Therefore, fromthe viewing area 20 the zone 62 and the area where there is orderedfield-on liquid crystal will appear relatively dark, i.e. as a darkbackground relative to the brightly colored illuminated liquid crystallayer 61 portion that is field-off and scattering. If desired, anabsorber (black or colored) may be used beyond the layer 91. Also, thecolor of background may be altered as a function of the thickness of thelayer 91.

Turning now to FIG. 9, an example of a liquid crystal device 100 inaccordance with the invention is shown in the form of a liquid cystaldisplay device, which appears as a square cornered figure eight 101within the substrate or support medium 12, which in this case preferablyis a plastic material, such as Mylar, or may alternatively be anothermaterial, such as glass, for example. The shaded area appearing in FIG.9 to form the square cornered figure eight is comprised of one or morelayers 61 of encapsulated liquid crystals 11 arranged in one or morelayers on and adhered to the substrate 12. An enlarged fragmentarysection view of a portion of the figure eight 101 is illustrated in FIG.4 as the display 60, 60' or 90 described above with reference to FIGS.4-8.

Each of the seven segments of the figure eight 101 may be selectivelyenergized or not so as to create various numeral characters. Forexample, energization of the segments 101a and 101b would display thenumeral "1" and energization of the segments 101a, 101b, 101c woulddisplay the numeral "7". What is meant by energization here is theplacing of the respective segments in a condition to appear as a brightcolor relative to background. Therefore, energization means field-off orrandom alignment condition of, for example, segments 101a and 101b todisplay "1" while the other segments are in field-on, ordered alignment.

FIGS. 10 and 11 illustrate, respectively in fragmentary section andfragmentary isometric-type views, an embodiment of the inventionrepresenting the preferred arrangement of the liquid crystal layer 61"and electrodes 13", 14" in the support medium 12". In FIGS. 10 and 11,double primed reference numerals designate parts corresponding to thosedesignated by unprimed reference numerals in FIGS. 4 and 5, or primedreference numerals in FIG. 6. In particular, it is preferred accordingto the illustration of FIGS. 10 and 11 that the display device 60" havethe layer 61" and the electrode 13" substantially continuous over theentire or at least a relatively large portion of a display device. Theelectrode 13" may be connected, for example, to a source of electricalground potential. The electrode 14" may be divided into a plurality ofelectrically isolated electrode portions, such as those represented at14a, 14b, each of which may be selectively coupled to a source ofelectric potential to complete application of an electric field acrossthat liquid crystal material which is between such energized electrodeportion 14a or 14b and the other electrode 13". Therefore, for example,an electric field may be applied across the electrodes 14a, 13" causingthe encapsulated liquid crystal material falling substantially directlytherebetween to be in ordered, field-on alignment and, thus, effectivelyoptically transparent in the manner described above. At the same time,it may be that the electrode 14b is not connected to a source ofelectric potential so that the liquid crystal material between suchelectrode 14b and the electrode 13" will be in distorted or randomalignment and, therefore, will appear relatively bright from the viewingdirection 20". A small gap 120 between electrodes 14a, 14b provideselectric isolation therebetween to permit the just-described separateenergization or not thereof.

Briefly referring to FIG. 12, the preferred embodiment and best mode ofthe present invention is shown as the display 60'". In FIG. 12 thevarious portions designated by triple primed reference numeralscorrespond to those portions designated by similar reference numerals,as are described above. The display device 60'" is made generally inaccordance with the numbered examples presented above. In particular,the lower support medium 12b'" is formed of Mylar film having an indiumdoped tin oxide Intrex electrode 13'" thereon; and the layer 61'" ofencapsulated liquid crystal material was applied to the electrode coatedsurface, as is shown. Several electrode portions 14a'", 14b'" etc. witha respective gap 120'" therebetween, were applied either directly to thesurface of the layer 61'" opposite the support medium 12b'" or to thesupport medium 12a'", and the latter was applied in the manner shown inFIG. 12 to complete a sandwich of the display device 60'". Moreover, thereflectance medium 80'" was air, and a carbon black absorber 21'"mounted on a support shown in FIG. 12 was placed opposite such air gap80'" from the support medium 12b'", as can be seen in the figure.Operation of the display device 60'" is according to the operationdescribed above, for example, with reference to FIGS. 4-6 and 10.

Referring to FIG. 13, an encapsulated liquid crystal 130 of the typedescribed herein is schematically shown. Such capsule 130 includes aspherical capsule wall 131 of containment material 132, operationallynematic liquid crystal material 133 inside the capsule, and acholosteric chiral additive 134. The additive 134 is generally insolution with the nematic material 13, although the additive is shown inFIG. 13 at a central location because its function primarily is withrespect to the liquid crystal material remote from the capsule wall, asis described further below. The capsule 130 is shown in field-off,distorted condition with the liquid crystal material distorted in themanner described above, for example, with reference to FIG. 2. Theliquid crystal material most proximate the wall 131 tends to be forcedto a shape curve like the inner boundary of that wall, and there is adiscontinuity 135 analogous to the discontinuity 55 shown in FIG. 2.

It will be appreciated that the encapsulated liquid crystal 130 of FIG.13 may be substituted in various embodiments of the invention describedin this application in place of or in conjunction with the otherwiseherein described encapsulated liquid crystal material. Operation wouldbe generally along the lines described in Examples 1 and 2, for example.

A modified liquid crystal display device 140 in accordance with thepresent invention is shown schematically in FIGS. 14 and 15. In thedevice 140 the primary source of illumination is derived from a lightsource 141 at the so-called back or non-viewing side 142 of the displaydevice. More specifically, the display device 140 includes a layer 61 ofencapsulated liquid crystal between a pair of electrodes 13, 14supported on upper and lower support media 12a, 12b generally in themanner disclosed above, for example with reflectance to FIG. 12. Thereference medium 80 is an air gap, as was described in connection withthe preferred embodiment above.

A light control film (LCF) sold by 3-M Company is shown at 143; the onepreferred is identified by product designationLCFS-ABRO-30°-OB-60°-CLEAR-GLOS-0.030. The light control film 143 is athin plastic sheet preferably of black substantially light absorbingmaterial that has black micro-louvers 144 leading therethrough from theback surface 145 toward the front surface 146 thereof. Such film or likematerial may be used in connection with the various embodiments of theinvention. Such film may in effect tend to collimate the light passingtherethrough for impingement on the liquid crystal material.

The micro-louvers function like a venetian blind to direct light fromthe source 141, for example light beams 150, 151, into and through thedisplay device 140, and particularly through the support medium 12 andliquid crystal layer 61, at an angle that would generally be out of theviewing angle line of sight of an observer looking at the display device140 from the viewing direction 20--this when the liquid crystal isaligned or substantially optically transparent. Such field-on alignedcondition is shown in FIG. 14 in which the light beams 150, 151 passsubstantially through the display device 140 out of the line of view.Moreover, light, such as light beam 152, incident on the display device140 from the viewing direction 20 will generally pass through thesupport medium 12 and aligned, field-on liquid crystal layer 61 forabsorption by the black film 143, which functions as the absorber 21'"in connection with FIG. 12, for example.

However, as is seen in FIG. 15, when the liquid crystal layer 61 is inthe field-off condition, i.e. the liquid crystal is distorted orrandomly aligned, the light beams 150, 151 from the source 141 areisotropically scattered by the layer of liquid crystal material 61causing total internal reflection and brightened colored appearance ofthe liquid crystal material in the manner described above. Thus, forexample, the beam 151 is shown being isotropically scattered as beam151a, totally internally reflected as beam 151b, and being furtherisotropically scattered as beam 151c which is directed out through theinterface 64 toward the viewing direction 20. The display device 140 ofFIGS. 14, 15 is particularly useful in situations where it is desirableto provide lighting from the back or non-viewing side. However, suchdisplay device also will function in the manner described above, forexample with respect to the display device 60'" of FIG. 12, even withoutthe back light source 141 as long as adequate light is provided from theviewing direction 20. Therefore, the device 140 may be used in daylight,for example, being illuminated at one or both sides by ambient lightwith or without the light source 141, and at night or in othercircumstances in which ambient lighting is inadequate for the desiredbrightness, for example, by using the illumination provided from thesource 141.

A display device 160 in FIG. 16 is similar to the display device 140except that the light control film 161 is cemented at 162 directly to,or is otherwise placed in abutment with the support medium material 12b.Total internal reflection would occur in the manner described above whenthe display device 160 is illuminated with light from the viewingdirection 20 due primarily to the interface 64 of the support medium 12awith air. There also may be some total internal reflection at theinterface 162. However, since the LCF film is directly applied to thesupport medium 12b, a relatively large quantity of the light reachingthe interface 162 will be absorbed by the black film. Therefore, in thedisplay device 160 it is particularly desirable to supply a backlighting source 141 to assure adequate illumination of the liquidcrystal material in the layer 61 for achieving the desired brightcolored character display function in accordance with the invention.

Briefly referring to FIG. 17, there is shown an alternate embodiment ofencapsulated liquid crystal material 200, which may be substituted forthe various other embodiments of the invention disclosed herein. Theencapsulated liquid crystal material 200 includes operationally nematicliquid crystal material 201 in a capsule 202 having preferably agenerally spherical wall 203. In FIG. 17 the material 200 is infield-off condition, and in that condition the structure 204 of theliquid crystal molecules is oriented to be normal or substantiallynormal to the wall 203 at the interface 205 therewith. Thus, at theinterface 205 the structure 204 is generally oriented in a radialdirection with respect to the geometry of the capsule 202. Moving closertoward the center of the capsule 202, the orientation of the structure204 of at least some of the liquid crystal molecules will tend to curvein order to utilize, i.e. to fill, the volume of the capsule 202 with asubstantially minimm free energy arrangement of the liquid crystal inthe capsule, for example, as is seen in the drawing.

Such alignment is believed to occur due to the addition of an additiveto the liquid crystal material 201 which reacts with the support mediumto form normally oriented steryl or alkyl groups at the inner capsulewall. More particularly, such additive may be a chrome steryl complex orWerner complex or other material that reacts with PVA of the supportmedium (12) that forms the capsule wall 203 to form a relatively rigidcrust or wall with a steryl group or moeity tending to protrude radiallyinto the liquid crystal material itself. Such protrusion tends to effectthe noted radial or normal alignment of the liquid crystal structure.Moreover, such alignment of the liquid crystal material still complieswith the above strongly curved distortion of the liquid crystalstructure in field-off condition because the directional derivativestaken at right angles to the general molecular direction are non-zero.

Briefly referring to FIG. 18 there is illustrated an embodiment of theinvention in which the dye is of the fluorescent type. Exemplaryfluorescent dyes may be an oil soluble fluorescent dye D-250 and a waterfluorescent dye may be that identified by the number D-834. In FIG. 18the oil soluble fluorescent dye 9F is shown in the oil base liquidcrystal material 30, and water soluble fluorescent dye 9F is shown inthe containment medium 33 and in the support medium 12. However, mostpreferably the fluorescent dye is in the containment medium; lesspreferably in the liquid crystal material, and least preferably in thesupport medium. However, the fluorescent dye may be in more than one ofsuch media or material.

Fluorescence is radiation caused by incident radiation. According to thepreferred embodiment and best mode of the invention, the fluorescedradiation or emitted radiation by the fluorescent dye is in or near thevisible light wavelengths. The light emitted by a fluorescing materialgenerally is emitted in an isotropic manner, i.e. it may not be possibleto predict the direction of the emitted light in response to incidentlight.

Referring particularly to FIG. 18, operation of the liquid crystaldevice 360 may be substantially the same as the other devices ordisplays described above the reference to the several figures. However,in response to an incident light beam, a fluorescent dye molecule orparticle will tend to fluoresce or to emit light itself, and this willoccur at the same time that the liquid crystal material in the layer 361is isotropically scattering light. In effect, then, there is a build-upof light level in the device 360, particularly when the liquid crystalmaterial in that layer 361 is in the scattering aligned mode, almostcharging up in a manner analogous to operation of a laser. Accordingly,the brightness, intensity, contrast, and/or other characteristics of theoutput light represented at 380 in FIG. 18 and viewed from the viewingdirection 320 is further enhanced. It will be appreciated that duringsuch operation the light isotropically scattered by the distorted liquidcrystal material and the emitted or fluoresced light will be totallyinternally reflected in the manner described above at the front and/orback interfaces of the device 360 to achieve the desired brightness.Also, that fluorescent dye which may be located in the support mediumand/or in the containment medium material that itself either is in thetransmissive mode or does not have therein liquid crystal material, forexample, as is indicated at the zone 362 in FIG. 18, and that light fromsuch dye, or at least most of that light, will be totally internallyreflected at the respective interfaces, as was described above.Therefore, such light either will be trapped in the support medium 312(except for the small quantity thereof that may be transmitted to theviewing direction 320, as above), or, alternatively, such fluorescedlight may be directed by total internal reflection onto distorted,scattering encapsulated liquid crystal material 311 in a layer 361providing a further light input thereto and, thus, brightening thereof.

EXAMPLE 3

The ingredients and method described above in Example 1 were employed,except that 0.4% (0.02 grams) of D-250 oil soluble fluorescent dye wasmixed with the oil base liquid crystal material before all of theingredients were combined. After the screening of the material, as wasdescribed above, a slide was taken. The slide was dried and under amicroscope it appeared that the capsules had a size of from about 3 toabout 4 microns. Moreover, a film of the thusly formed emulsion waspulled using a doctor blade set at a gap 5 setting; such film wasapplied to a Mylar substrate having an Intrex electrode thereon. Inoperation, full scattering occurred prior to 8 volts of an electricfield; at 8 volts scattering began to reduce; and at 25 volts saturationwas achieved.

EXAMPLE 4

The ingredients and method described above in Example 1 were employed,except that 0.4% (0.06 grams) of D-834 water soluble fluorescent dye wasmixed with the water base liquid crystal material before all of theingredients were combined. After the screening of the material, as wasdescribed above, a slide was taken. The slide was dried and under amicroscope it appeared that the capsules had a size of from about 3 toabout 4 microns. Moreover, a film of the thusly formed emulsion waspulled using a doctor blade set at a gap 5 setting; such film wasapplied to a Mylar substrate having an Intrex electrode thereon. Inoperation, full scattering occured prior to 8 volts of an electrodefield; at 7 volts scattering began to reduce; and at 25 volts saturationwas achieved.

EXAMPLE 5

The ingredients and method described in Example 3 were employed exceptthat 0.4% Congo Red dye was substituted for the D-250 dye. The resultswere similar; threshold was at 9 volts, and saturation was at 30 volts.

The fluorescent dye may be used in and/or with the several otherembodiments and features of the invention disclosed herein.

The invention may be used in a variety of ways to effect color displayof data, characters, information, pictures, etc. or simply light controlon both small and large scale. The invention envisions use ofnon-pleochroic dye in one or more of the media or materials describedabove, although most preferably according to the present best mode thedye is in the containment medium. According to one embodiment and bestmode of the invention, the liquid crystal material is placed in thesupport medium 12 at only those areas where characters, etc., are to beformed. In the alternative, the layer 61 may extend across the entiresupport medium 12, and only those areas where characters are to bedisplayed will have electrodes for controlling field-on/field-off withrespect to the proximate portions of the liquid crystal layer 61. As anoptical shutter, the invention may be used to adjust the effectiveand/or apparent brightness of light viewed at the viewing side. Variousother designs also may be employed, as may be desired, utilizing theenhanced scattering effected by the total internal reflection and/oroptical interference principles in accordance with the present inventionincluding, for example, optical shutters, billboards, etc., which may beconsidered included in the definition of "display" as used herein.

STATEMENT OF INDUSTRIAL APPLICATION

The invention may be used, inter alia, to produce a controlled opticaldisplay.

I claim:
 1. Liquid crystal apparatus comprising liquid crystal means for selectively primarily scattering or transmitting light in response to a prescribed input, a support medium means for holding therein such liquid crystal means, said support medium means having a characteristic of total internal reflection, and dye means in at least one of said liquid crystal means and said support medium means for coloring light transmitted therein.
 2. The apparatus of claim 1, said support medium means comprising a containment medium means for forming with said liquid crystal means encapsulated liquid crystal and a support means for supporting said encapsulated liquid crystal, said support means having a viewing angle and an opposite side.
 3. The apparatus of claim 2, the index of refraction of said support means being greater than the index of refraction of at least one of the media respectively at such viewing and opposite sides forming an interface therewith to effect total internal reflection of light in said support means incident on such interface at an angle exceeding a predetermined cone of light angle at which light would be transmitted through such interface.
 4. The apparatus of claim 2, said dye comprising nonpleochroic dye dissolved in said liquid crystal means.
 5. The apparatus of claim 2, said dye comprising a fluorescent dye.
 6. The apparatus of claim 5, said fluorescent dye being nonpleochroic.
 7. A method of making a liquid crystal apparatus comprising placing an encapsulated liquid crystal material in or on a support medium, and placing a dye in at least one of such encapsulated liquid cystal material and support medium.
 8. The method of claim 7, said placing a dye comprising placing a non-pleochroic dye in such encapsulated liquid crystal material.
 9. The method of claim 8, such encapsulated liquid crystal material comprising a containment medium containing discrete volumes of liquid crystal material, said placing a dye comprising mixing a dye directly in such liquid crystal material.
 10. The method of claim 7, wherein such support medium has a substantial internal reflection characteristic, and further comprising providing a further medium at an interface with such support medium and selecting the index of refraction of such support medium to be greater than the index of refraction of such further medium, whereby total internal reflection of light will occur in such support medium with respect to light impinging on such interface at an angle less than a predetermined angle with respect to normal.
 11. The method of claim 10, further comprisng applying a light absorbing material beyond such further medium for absorbing light transmitted through such further medium.
 12. The method of claim 7, further comprising applying a tuned dielectric interference layer to a surface of such support medium opposite the surface at which such support medium ordinarily is viewed.
 13. The method of claim 7, said placing a dye comprising placing a fluorescent dye.
 14. An optical apparatus for providing a color output comprising an operationally nematic liquid crystal in a support medium and a non-pleochroic dye, said operationally nematic liquid crystal material in a support medium comprising an emulsion of said liquid crystal material and a containment medium.
 15. The apparatus of claim 14, further comprising additive means in said operationally nematic liquid crystal material for expediting such distorting and return to random alignment upon the removal of such electric field.
 16. The apparatus of claim 14, further comprising chloroform.
 17. The apparatus of claim 14, further comprising a surfactant.
 18. The apparatus of claim 17, said surfactant comprising a non-ionic surfactant.
 19. The apparatus of claim 14, further comprising an aligning means at least partly reactive with said containment medium means to align in relatively fixed position with respect thereto, and said aligning means being so positioned with respect to the capsule-like walls of said volumes and with respect to said liquid crystal to align at least part of at least some of the latter substantially normal with respect to said wall.
 20. The apparatus of claim 19, said aligning means comprising a chrome alkyl complex.
 21. An optical apparatus for providing a color output comprising an operationally nematic liquid crystal in a support medium and a non-pleochroic dye, said liquid crystal comprising at least one layer of liquid crystal material in a containment medium that tends to distort at least some of the liquid crystal material to align generally with respect to a wall of such containment medium when in the absence of an electric field, and said liquid crystal material being responsive to an electric field to tend to align with respect thereto.
 22. The combination of operationally nematic liquid crystal material contained in a generally spherical capsule of encapsulating medium, said encapsulating medium having a wall, the ordinary index of refraction of said liquid crystal material being approximately the same as the index of refraction of the encapsulating medium, and non-pleochroic dye in at least one of said liquid crystal material and encapsulating medium, said containment medium comprising a water base material, and said dye comprising a water soluble dye dissolved in said containment medium, said dye comprising fluorescent dye.
 23. The combination of operationally nematic liquid crystal material contained in a generally spherical capsule of encapsulating medium, said encapsulating medium having a wall, the ordinary index of refraction of said liquid crystal material being approximately the same as the index of refraction of the encapsulating medium, and non-pleochroic dye in at least one of said liquid crystal material and encapsulating medium, said liquid crystal material comprising an oil base material, and said dye comprising an oil soluble dye dissolved in said liquid crystal material said dye comprising fluorescent dye. 